Method for imaging measurement, imaging measurement device and use of measured information in process control

ABSTRACT

The invention relates to method for imaging measurement of a moving or flowing target and to an imaging measuring device for implementing the aforementioned method. Moreover, the invention relates to the use of information measured by means of imaging measurement in the control and/or adjustment of a process. According to the invention, electromagnetic radiation obtained from the moving or flowing target (T) is focused by means of imaging optics to produce an image to the screen of a two-dimensional matrix detector at least via a first and a second filter (F 1 , F 2 ) which transmit electromagnetic radiation in manners differing from each other. Said at least first and second filter form on the screen of the detector at least a first and a second filter area (FR 1 , R 2 ) that partly cover the light-sensitive area (DA) of the detector. The properties of the target (T) are determined spectroscopically by comparing and/or combining spectrally resolved information, which is recorded when a pixel which corresponds to a determined part of the target kto be measured and is focused on the screen (DA) of the matrix detector without beamsplitting travels under the effect of the movement of the target (T) via said at least first and second filter area (FR 1 , FR 2 ). The area of the screen (DA) of the detector remaining outside siad filter areas (FR 1 , FR 2 ) is used for other kind of imaging non-spectroscopic measurement and/or visualization of the target.

FIELD OF THE INVENTION

The invention relates to method for imaging measurement of a moving orflowing target. The invention also relates to an imaging measuringdevice. Moreover, the invention relates to the use of informationmeasured by means of imaging measurement in the control and/oradjustment of a process.

BACKGROUND OF THE INVENTION

In many technical processes it is advantageous to be able to measure thedifferent parameters of the process in real time to examine, monitor andcontrol said processes without disturbing the course of the process orstate of the process itself. Optical measuring methods which are basedon determining the state or properties of the target on the basis of theelectromagnetic radiation (later shortly radiation) obtained from thetarget, offer according to their basic nature a possibility fornon-intrusive measurements. Methods based on conventional physicalprobes, such as measurements using thermocouples (temperaturemeasurement) or different methods based on sampling (e.g. concentrationmeasurements) always disturb the target to be measured to a certaindegree. When compared to traditional physical probes, by means ofoptical methods it is in many cases possible to conduct the measurementswith a significantly better temporal and spatial resolution. It is alsoadvantageous to use optical methods in connection with such processes inwhich the use of physical probes is impossible or difficult because ofhigh temperatures prevailing in the process or other conditions hostileto the physical probes.

Optical measuring methods can be divided into different classes by meansof various criteria. If the instantaneous spatial resolution attained bymeans of optical measuring methods is used as a comparison criterion, itis possible to divide the methods to non-imaging and imaging methods onthe basis of this criterion. The basic differences between these methodsare shortly described in the following.

In imaging methods the detector that is utilized is a suitabletwo-dimensional, spatially resolving detector (hereinbelow shortlymatrix detector), wherein the electromagnetic radiation obtained fromthe target by means of suitable front optics is collected and focused onthe light-sensitive screen of the aforementioned detector. In thewavelength range of visible light the matrix detector may be for examplea so-called CCD or CMOS camera. The screen of the aforementioneddetector is composed of separate small light-sensitive detector units(hereinbelow pixels), of which each pixel collects the radiationtransmitted by a fixed part of the target according to the imagingproperties of the front optics. When the radiation signalcollected/detected by the aforementioned pixels during a predeterminedintegration time is changed into an electric form in such a manner thatthe pieces of information contained in different pixels are kept apartfrom each other, spatially resolved information is obtained from thearea of the target that is imaged in the aforementioned manner, saidinformation being collected from the entire area either exactly orsubstantially at the same time, depending on the structure and operatingmode of the used detector.

In non-imaging methods the radiation is typically detected by means ofonly one such detector, such as a photo diode or a photomultiplier tubein which the radiation entering on the light-sensitive or radiationsensitive surface of the same produces an electric signal that cannot betraced as a function of the spatial location of the screen of thedetector and thus, more specifically, as a function of the location ofthe radiation signal collected by said detector from the target. Thus,the properties of front optics are typically selected either in such amanner that radiation signal is collected simultaneously on the entirearea of interest of the target, or alternatively in such a manner that asmaller measuring point detected by the detector in the target istemporally scanned to different sections of the target to obtainspatially resolved measurement information. In the latter case theinformation obtained from different sections of the target is, however,measured substantially at different moments in time, which is asignificant restriction in cases where rapidly changing processes whichare spatially heterogeneous are used.

The rapid development of detector technology and especially thedevelopment of matrix detectors both in the visible light range(wavelength range of approximately 300 to 800 nm) and in the ultravioletrange (<300 nm) and in infrared (>800 nm) has enabled a strong increasein the use of imaging measuring methods in research, monitoring andcontrol operations of different processes applied in the industry.Together with the development of computer and image processingtechnologies enabling a more efficient processing of image information,the aforementioned matrix detectors nowadays make it possible to developimaging measuring methods which function substantially in real-time.

Imaging optical measuring methods can be further divided intonon-spectroscopic and spectroscopic methods. In non-spectroscopicimaging methods which typically include most of the conventional machinevision methods (the parameter to be measured for example the size,location or position of the target), the electromagnetic radiationobtained from the target is not divided especially according to thewavelength of radiation, but the radiation is detected typically only inone wavelength band. This wavelength band may be determined for exampleaccording to the radiation used for illuminating the target, and/oraccording to the natural spectral operation range of the matrix detectorused in the measurement. It must be noted that in this text the termoptical does not refer solely to the wavelengths of visible light(approximately 300 to 800 nm), but radiation with a substantiallyshorter (ultraviolet range) or longer wavelength (infrared range) thanvisible wavelength is also possible.

In spectroscopic methods, i.e. in methods based on spectral resolutionthe radiation obtained from the target is, however, divided into two ormore spectral bands differing from each other, wherein by comparingand/or combining the signals/images measured at different wavelengthbands it is possible to determine parameters of interest in the target,such as local temperature, or local concentration of a particularcomponent of interest. More commonly used spectroscopic methods whosebasic principles are known are for example two-color or multicolorpyrometry, by means of which it is possible to determine the temperatureof the target on the basis of the electromagnetic radiation emittedspontaneously by the target. By means of a suitable external stimulus(e.g. laser light or so-called spectral lamps) it is also possible toconduct measurements based on optical absorption, or elastic (e.g.so-called Mie scattering from particles/droplets) or nonelastic (e.g.so-called fluorescence or Raman scattering) scattering of radiation,such as concentration measurements. The principles of theabove-mentioned spectroscopic methods, which in this context includepyrometry as well, are generally and widely known, and therefore theywill not be discussed in more detail herein since they do not form apart of the actual invention.

To implement the aforementioned spectroscopic methods, it is oftennecessary to use spectrally resolved information measured at least ontwo wavelength bands to define the parameter of interest in the target.In imaging methods this usually means that the spectral bands resolvedfrom each other by means of a beamsplitter/beamsplitters and differentoptical filters are guided to a separate matrix detector each, oralternatively all spectral bands are guided to the same matrix detectorin such a manner that the signals produced by them can be distinguishedfrom each other.

Naturally, in spectrally resolving imaging measurements intended forindustrial conditions and applications, the above-described use ofseveral separate matrix detectors is problematic in that respect thatsaid measuring devices have a complex structure and they are expensive.Therefore, a more interesting solution in view of industrialapplications is the use of a single matrix detector for detecting allspectral bands to be measured and at the same time the attempt to reducethe number of optical components required in resolving said spectralbands and focusing them to the light-sensitive screen of the detector aswell as to minimize the adjustments required in positioning thesecomponents, i.e. to simplify the structure, implementation and use ofthe measuring device. In industrial conditions another significantfactor is also the compact mechanical structure of the measuring devicewhich is attained in the above-described manner and which enduresexternal conditions well.

The following is a description of known solutions that can be used withspectroscopic measuring methods and which enable imaging spectralresolution.

Patent publication U.S. Pat. No. 4,413,324 discloses three differentways of implementing spectrally resolved imaging measurement by means ofmatrix detectors. More precisely, the measurement in question is animaging pyrometric two-color temperature measurement of a target,conducted by means of two measurement wavelength bands differing fromeach other. The first method described in the aforementioned publicationis based on the use of optical filters of two different types placed infront of the screen of one matrix detector (camera), the spectral bandsof the filters differing from each other. The aforementioned filters,the size of each of them advantageously corresponding exactly to thesize of a single pixel in the detector, together form a continuousmosaic filter that covers the light-sensitive screen of the matrixdetector entirely. A second method disclosed in the same publication isbased on the temporal measurement of spectral bands at different momentsin time by using a disc to be rotated in front of one matrix detector,said disc being composed of two different optical filters to attainspectral resolution. A third method disclosed in said patent publicationis based on the act of dividing the radiation attained from the targetinto two spectral bands differing from each other, each band beingguided to separate matrix detectors of their own. It is characteristicto all the methods disclosed in the patent publication U.S. Pat. No.4,413,324 that two separate spectral bands are used in them and that thedetector/detectors uses/use the entire imaging area for only onemeasuring method.

Patent publication U.S. Pat. No. 5,963,311 discloses another type of adevice suitable for imaging two-color pyrometry, in which the radiationreceived from the target is divided into two parts, which parts areguided through different optical filters further to a matrix detector insuch a manner that the images corresponding to different filters andrepresenting different wavelength bands, which both correspond to thesame area imaged from the target, are formed on the screen of the matrixdetector adjacently with respect to each other. In the method disclosedin said publication the radiation received from the target is first usedto form an image in the so-called intermediate focus of the optics, fromwhich it is imaged on the screen of the actual detector. The use of theintermediate focus enables the adjustment of the magnification of thetwo adjacent images formed on the screen so that the magnification isequal in both images, as well as a better control of scattered lightbetween said images.

Patent publication U.S. Pat. No. 5,225,883 discloses an arrangementsuitable for imaging two-color pyrometry of a stationary ormoving/flowing target. Similarly to the method disclosed above in thepatent publication U.S. Pat. No. 5,963,311, in this case the radiationreceived from the target is divided into two parts, which parts areguided through different optical filters further to a matrix detector insuch a manner that the images corresponding to different filters andrepresenting different wavelength bands, which both correspond to thesame area imaged from the target, are produced on the screen of thematrix detector adjacently with respect to each other. When compared tothe solution disclosed in the publication U.S. Pat. No. 5,963,311, thesolution presented in the publication U.S. Pat. No. 5,225,883 does notapply an intermediate focus in the adjustment of magnification, but inthe other optical arm an optic component with a suitable refractiveindex is utilized to compensate the path length difference between theoptical arms corresponding to the images, thus enabling the focusing ofsaid two images on the screen of the detector by means of magnificationwhich is exactly equal in both images.

It is characteristic to all above-presented imaging solutions thatenable a substantially simultaneous spectrally resolved measurement onseveral spectral bands that the division and/or filtering of theradiation attained from the target into spectral bands that differ fromeach other takes place in such a manner that said process is conductedin the same way for the area imaged from the entire target, and theentire imaging area of the matrix detector/matrix detectors is thus usedfor the same spectroscopic measurement, such as two-color pyrometry.Thus, it is a drawback and a considerable restriction of theaforementioned methods in imaging measurements based on spectralresolution that they can be advantageously used only for spectroscopicmeasurements of one type at a time without changing or adjusting theoptical components. Furthermore, the filters selected for a particularspectroscopic measurement are not optimally suitable for merevisualization of the target, or other non-spectroscopic measurements.

Moreover, it is a problem in the above-presented known solutions that itis necessary to use several optical components therein to divide and/orfilter the light obtained from the target into different spectral bandsand to focus it to the matrix detector, which said components must, inmost cases, be adjusted and focused with great accuracy with respect toeach other and/or the matrix detector. Especially in those knownsolutions in which the images measured on different spectral bands thatcorrespond to the same location in the target, are projected separately(U.S. Pat. Nos. 5,963,3115, 5,225,883) next to each other on the screen,the picture elements corresponding to a particular part of the target ondifferent wavelength bands in the matrix detector are located far awayfrom each other. This complicates a reliable mutual identification ofsaid picture elements, and it sets special requirements in view offocusing and adjusting said optical components, so that magnificationsof images measured on different wavelengths become equally large insize. Correspondingly, a preferred embodiment of the mosaic filterdisclosed in the patent publication U.S. Pat. No. 4,413,324 requiresthat each single filter is positioned accurately to correspond to one orseveral pixels of the detector. This is technically challenging andtherefore expensive especially in cases of smaller production batches.

In view of the present invention, the solution disclosed in the patentpublication U.S. Pat. No. 5,225,883 can be considered as the closeststate of the art solution among the above-presented prior art solutions,and in said publication the suitability of the solution for measurementof moving or flowing target is also emphasized. Said publication doesnot, however, in any way mention the possibility of utilizing themovement of the target for recording spectrally resolved information andfurther for conducting spectroscopic measurement in a manner intended bythe invention disclosed in the present application.

SUMMARY OF THE INVENTION

The purpose of the present invention is to eliminate the above-describedrestrictions and problems of prior art when imaging spectrally resolvedmeasurements are conducted for such processes which include a moving orflowing target. One aim is to introduce a method which has a simplerstructure when compared to prior art, and which can be implemented witha smaller number of components and adjustments and by means of whichspectrally resolved imaging measurements can be conducted in a morereliable and economical manner especially in industrial processconditions demanding in view of the mechanical durability of themeasuring device. Another aim is to enable optimal measurement ofseveral spectroscopic and/or non-spectroscopic parameters and/or merevisualization of the target by using a single compact measuring devicewithout having to conduct changes of components, such as optical filtersin the measuring device and/or other significant modifications ormechanical adjustments.

To attain this purpose, the present invention provides an imagingmethod, an imaging device, and a use of information measured by imagingmeasurement in process control and/or adjustment as described herein.

The invention is characterized by the new, inventive feature thatconsiderably simplifies and facilitates the implementation of spectrallyresolving spectroscopic imaging measurements and the measuring devicesnecessary therein as well as the use of said measuring devices.According to the invention the movement of the target to be measureditself is utilized to record spectrally resolved signals to be measuredat wavelength bands differing from each other. This is attained byrecording signals which are produced when an image point which isfocused on the screen of the matrix detector without beam splitting andwhich corresponds to a fixed part of the target to be measured travelsunder the effect of the movement of the target via filter areastransmitting radiation in manners differing from each other. In otherwords, the spectroscopically measured parameter of a particular part ofthe target is defined using imaging together with comparison and/orcombining information received from the different filter areas in theaforementioned manner. In such imaging taking place withoutbeamsplitting the image of the target is not duplexed etc. on the screenof the detector, and therefore at a fixed moment of time only one imagepoint corresponds to a single small part of the target.

Said filter areas are attained by means of filters with a simplestructure which are placed substantially immediately in front of thedetector, or which are placed in the intermediate focus of the appliedfront optics. Because according to the invention said filter areas canhave a large area compared to the size of single pixels of the matrixdetector, each filter area therefore advantageously covering hundreds orthousands of single pixels, it is possible to align and adjust them withrespect to each other and to the detector in a simple manner and it isnot necessary to specially align the filter areas to correspond tocertain individual pixels in the detector. The aforementioned propertiesmake it possible to manufacture measuring devices according to theinvention profitably in small product batches optimized for differentpurposes of use.

It is characteristic to the invention that said filter areas necessaryfor spectroscopic measurement cover the screen of the matrix detectoronly partly, wherein the remaining part of the imaging area of thedetector can be used for other non-spectroscopic measurements and/orvisualization of the target. In the monitoring of an industrial process,it is often advantageous to conduct mere visualization of the target, inother words to transmit unprocessed or only slightly processed real-timeimage to the operator monitoring/adjusting the process. In themethod/device according to the invention this can be easily implementedby utilizing the imaging area of the matrix detector which is eitherunfiltered or filtered in a manner suitable especially forvisualization. By utilizing the possibility of visualization, theimaging area monitored/measured of the target can be easily defined bythe operator, in other words the imaging device can be easily andaccurately focused to a desired target area.

When compared to prior art, in the solution according to the invention,if necessary, it is also easy and simple to use more than two filtersthat filter the radiation in different manners. Correspondingly, thisenables substantially simultaneous use of more than one spectroscopicmeasuring method without need for changing and/or adjusting the opticalcomponents but still maintaining the spectral bands to be used alwaysoptimally selected for a given purpose and spectroscopic measurement.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the invention will be described in more detail withreference to the appended drawing, in which

FIG. 1 shows a side-view of an arrangement according to the inventionfor conducting spectrally resolved measurement of a moving or flowingtarget,

FIG. 2 shows a side-view of an alternative arrangement according to theinvention for conducting spectrally resolved imaging measurement of amoving or flowing target,

FIG. 3 shows an arrangement of filter areas formed according to theinvention on the imaging area of a matrix detector when seen from thedirection of front optics perpendicularly to the screen of said matrixdetector,

FIG. 4 shows in a manner similar to FIG. 3 different alternativearrangements of the filter areas according to the invention on theimaging area of the matrix detector,

FIG. 5 shows a solution according to the invention in monitoring athermal spray coating process,

FIG. 6 shows in the situation according to FIG. 5 the image produced bythe particle jet on the matrix detector when the exposure time used inthe detector is short in relation to the velocity of the coatingparticles,

FIG. 7 shows in the situation according to FIG. 5 the image produced bythe particle jet on the matrix detector when the exposure time used inthe detector is long in relation to the velocity of the coatingparticles,

FIG. 8 shows how the parameter defined from the target by means offilter areas is utilized to produce a local distribution of saidparameter, transverse to the motion of the target,

FIG. 9 shows how the parameter defined from the entire imaging area inthe target is utilized to produce a local distribution of saidparameter, transverse to the motion of the target, and

FIG. 10 shows how the parameter defined from the entire imaging area inthe target is utilized to produce a local distribution of saidparameter, parallel to the motion of the target.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows in a side view an arrangement according to the invention inwhich an image is formed of a moving or flowing target T by means ofimaging optics L1 and via filters F1, F2 on the screen D of atwo-dimensional matrix detector, which matrix detector, furthermore, isplaced in a camera C. FIG. 2 shows an alternative arrangement accordingto the invention in which an image of the target T is produced by meansof imaging optics L2 on filters placed on the intermediate focus of theoptics L2 and L3, which image formed in the intermediate focus andtravelling via the filters F1, F2 is further transferred to the screen Dof the matrix detector by means of the optics L3.

The moving or flowing target T shown in FIGS. 1 and 2 (andcorrespondingly in FIGS. 3 to 4) can be a target with a substantiallyhomogenous solid structure, substantially homogenous liquid structure orsubstantially homogenous gaseous structure, such as for example a hot,glowing metal object undergoing a rolling-mill practice, or a flow orflame produced by molten metal. The target may also have a heterogeneousstructure, such as a gas flow containing solid or liquid particles, orcorrespondingly a liquid flow containing gas bubbles or solid particles.The temperature of the target can be any temperature as such, which istypical for the process under examination.

In FIGS. 1 and 2, the imaging optics L1, L2, L3 can be composed of oneor several separate lenses each, or each optics L1, L2, L3 can be aso-called camera objective containing several lenses, which can furthercontain means for focusing the image on the matrix detector D, ifnecessary, as well as means for limiting the aperture of said optics tocontrol the depth of focus and level of brightness of imaging. If theimage is relayed on the matrix detector D via more than one intermediatefocuses, there may be several imaging optics in use, if necessary, andthey can be contained for example in an endoscope or anothercorresponding special optics used as front optics. If necessary, theimaging optics may also contain so-called field lenses placed in theimmediate vicinity of the focal planes to improve the quality of theimage.

The imaging optics L1, L2, L3 and the filters F1, F2 do not have to belocated on the same straight optical axis, but it is also possible touse mirrors, if necessary, to deflect the direction of the optical axis,or the optics L1, L2, L3 themselves can also be implemented by utilizingconcave ball mirrors, and, furthermore, the filters (when placed in theintermediate focus) can be implemented as reflecting components as well,if necessary.

In a situation according to the invention and seen from the direction ofthe imaging optics (L1 in FIG. 1 and L3 in FIG. 2) and perpendicular tothe screen D of the matrix detector, FIG. 3 shows the filter areas FR 1and FR2 formed on the light-sensitive area DA of said screen by means offilters F1, F2. In FIG. 3 broken lines also illustrate in principle howthe moving or flowing target T is imaged on the screen D in situationsaccording to FIG. 1 or 2.

FIG. 4 shows in a manner corresponding to FIG. 3 some alternative waysof arranging the filter areas according to the invention on the imagingarea of the matrix detector. FIG. 4 a shows an arrangement of two filterareas FR1 and FR2 which are small in size with respect to the surfacearea of the light-sensitive area DA of the detector and which filterareas are in contact with each other. FIG. 4 b shows filter areas FR1and FR2 which are not contacting each other, as well as filter areas FR3and FR4 located on the other edge of the imaging area, wherein theproperties of the filter FR3 correspond to those of filter FR1 and theproperties of filter FR4 to those of filter FR2. Furthermore, FIG. 4 cshows an arrangement of two non-rectangular filter areas whose sizesdiffer from each other. FIG. 4 d further shows an arrangement of threefilter areas FR1, FR2, FR3 that transmit radiation in different manners.

The invention is not restricted to the above-described ways of arrangingthe filter areas on the imaging area of the detector, but the size,shape and number of the filter areas can vary according to theembodiment in question in such a manner that under the effect of themovement of the target, an image point on the screen of the detectorthat corresponds to a certain part of the target, however, substantiallytravels via the filter areas necessary in the spectroscopic measurementin question.

To produce the filter areas on the screen D of the detector, the filtersF1, F2 can be composed of uniform substrate material substantiallytransparent in the operating wavelength area of the detector, whosefront and/or back surface/surfaces are/is at desired locations providedwith a coating that reflects, absorbs or otherwise attenuates theradiation of the target in a desired manner, for example with aso-called dichroic multilayer coating. Alternatively, the filters F1, F2can be made by replacing the desired areas in the above-mentioned,substantially transparent substrate material with a material thatabsorbs or otherwise attenuates the radiation in a desired manner, forexample with a colored glass. Furthermore, the assembly containing thefilters F1, F2 can be formed in such a manner that it does not containany actual substrate material at all in those parts in which the aim isnot to affect the properties of radiation travelling therethrough, butthe filter structures F1, F2 corresponding to the actual filter areasFR1, FR2, which are formed in any of the ways described above, areattached separately directly on the screen of the detector D (thesituation shown in FIG. 1), or the aforementioned filter structures F1,F2 are attached and positioned with respect to each other by means of asuitable mechanical member, such as wiring (the situation shown in FIG.2), said member itself having as thin a structure as possible so that itdisturbs the transmission of radiation as little as possible. Thefilters F1, F2 can contain/have a structure of a so-called diffractivecomponent, in which the areas corresponding to the different sections ofthe light-sensitive area DA of the detector are manufactured in desiredshapes and in the desired manner to form filter areas according to theinvention on the screen of the detector D. The filters can also beformed by combining the aforementioned different structural solutionsand furthermore, the filters corresponding to the different filter areascan be located at different locations for example in such a manner thatthe first filter F1 is placed in front of the detector D (according toFIG. 1) and the second filter F2 is placed in the intermediate focus ofthe front optics (according to FIG. 2). Furthermore, the filter areasFR1, FR2 formed on the light-sensitive area DA of the detector can beproduced by means of such filter element whose transmission/reflectionchanges as a function of place in such a manner that at a particularpoint of the filter element the transmission/reflection of the samecorresponds to the filter F1 and at another point to the filter F2. Thefilter element of said kind that contains a changing/sliding spectralresponse can be manufactured by using the aforementioned structuralsolutions, for example by means of dichroic coatings.

The two-dimensional matrix detector D, which is positioned in the cameraC, can be for example a so-called CCD detector, which, being asilicon-based detector, operates in the wavelength range of 200 to 1100nm, and it can contain a so-called electric shutter function to controlpixel exposure. In CCD detectors of this kind the number of pixels can,for example, in a ⅔-inch detector be 1280 pixels in the horizontaldirection and 1024 pixels in the vertical direction, wherein the size ofsingle pixels is for example 6.7 micrometers multiplied with 6.7micrometers. Depending on the embodiment, the detector can, however, bea matrix detector of another type in which the size of thelight-sensitive imaging area of the detector and the number of pixelscan vary, and the shutter time of the detector can be adjusted by usinga separate external mechanical or electro-/magneto-optic shutter. Inwavelength ranges of 900 to 1700 nm, the detector can be for example a1-inch matrix detector of 320 pixels×240 pixels, made of InGaAssemiconductor. The detector can also be a so-called CMOS detector.Furthermore, all pixels of the matrix detector can contain an equalspectral wavelength response, or different pixels can contain adifferent spectral wavelength response. In other words, the detector canalso be for example a colour camera. The exposure times of the differentpixels of the detector can be adjusted in different ways betweendifferent pixels by means of an internal electric shutter function.Similarly, in the camera the gain of the electric signal to be read fromdifferent pixels of the detector can be adjusted in different waysbetween different pixels, and the signals of several adjacent pixels canbe added together before reading by means of a so-called binningfunction.

The camera C to which the matrix detector D is placed takes care ofchanging the optical signal collected by the detector to an electricformat and controls the electric functions of the detector as well. Theaforementioned control commands can arrive directly from a computer inan electric format or manually via switches set by the user in thecamera. The camera C can be a so-called digital camera in which theimage captured by the detector is changed already in the camera itselfinto a digital format expressed by a binary code, which binaryinformation is transmitted further to the actual measuring computer forimage processing and calculation to be conducted at a later stage.Alternatively, the camera C can also be a so-called analog video camerafrom which the image captured by the detector is transmitted first as ananalog video signal to a computer, in which the analog signal is changedinto digital format for example by means of a suitable so-called imagecapture card. It is also possible that the camera C can contain amicroprocessor of its own or corresponding circuit/circuits so thatimage processing can be conducted entirely or partly already in thecamera before information is transmitted forward.

In the following, the invention will be described further in moredetail, using the use of the invention in the control of a thermal spraycoating process as an example.

FIG. 5 illustrates the principle of a thermal spray coating process.Coating material is fed in a powder form from a feeding port I to thehot gas flame P flowing from the spraying device G. Said gas flame canbe a so-called plasma flame produced by means of an electric arc, or agas flame generated by burning of reactive gas components. In the flameP, the coating particles melt and they are accelerated to a certainvelocity before they impact on the target S to be coated. When themolten or partly molten coating particles impact on the target to becoated they flatten and cool down into thin lamellas. The layering ofthe aforementioned lamellas on the surface of the target S forms thedesired coating. Known thermal spray coating processes that are widelyused industrially include for example plasma spraying, HVOF spraying,detonation spraying and flame spraying. By means of these sprayingmethods it is possible to manufacture for example metal, ceramic orplastic coatings for widely varying purposes.

In thermal spraying the in-flight properties of the coating particlesjust before they impact on the target to be coated are essential in viewof the properties and quality of the coating to be produced. In thisrespect the most important parameters of the coating particles are thetemperature, velocity, number and size of the particles, as well as thelocal distribution of these parameters in the flame.

The method according to the invention enables both imaging spectroscopicand imaging non-spectroscopic measurements by means of the samemeasuring device, as well as also in-flight visualization of the coatingparticles/particle jet before the particles/particle jet impacts on thetarget S to be coated. In FIG. 5 broken lines show an imaging region ROIsuitable for such process monitoring. In this example, the parameter tobe measured spectroscopically according to the examples describedhereinbelow is the pyrometric two-color temperature of the coatingparticles, and parameters to be determined non-spectroscopically includee.g. the velocity and instantaneous number of the coating particles. Asa result of the imaging method it is possible to obtain spatiallyresolved information of the aforementioned parameters, i.e. localdistributions of said parameters from the imaging region ROI.

FIG. 6 shows the image produced by the hot coating particles on thematrix detector in a situation where the exposure time used in thedetector is short in relation to the velocity of the coating particles.Thus, individual coating particles are imaged as separate streaks on thelight-sensitive area DA of the detector by means of the thermalradiation emitted by the coating particles themselves, the length of thestreaks depending on the used exposure time and the velocity of theparticles. In FIG. 6 one such streak produced by one coating particle ismarked with T1. When filter areas FR1 and FR2 are arranged on theimaging area of the detector according to FIG. 6, spectrally resolvedinformation is attained on the two wavelength bands corresponding tosaid filter areas from the emission of individual particles passing theborder between said filter areas during the exposure time. Themeasurement takes place in such a manner that the time differencebetween the measurements for the individual particles on said twowavelength bands is shorter than the exposure time used in the imaging.When said two wavelength bands are selected in a suitable manner it ispossible to use the emission measured by means of the same to determinethe two-color pyrometric temperature of individual coating particleswith the assumption that the temperature of the particles does notsubstantially change within the scope of the exposure time used in theimaging. Typically for example in plasma spraying the velocities ofcoating particles are often hundreds of meters per second, wherein, inpractice, the situation according to FIG. 6 is attained by usingexposure times in the order of microseconds. By means of imageprocessing techniques it is easy to identify the different parts of thestreaks (e.g. T1) shown in FIG. 6 that are measured at differentwavelengths and located close to each other, when compared to methods inwhich images corresponding to the same area of the target, for example aparticle, and measured at different wavelengths are located relativelyfar from each other on the light-sensitive area DA of the detector (e.g.U.S. Pat. Nos. 5,963,311 and 5,225,883).

FIG. 7 shows in a corresponding manner the image produced by hot coatingparticles on the matrix detector in a situation where the exposure timeused in the detector is long in relation to the velocity of the coatingparticles. Thus, the measuring result obtained from the filter areas FR1and FR2 contains measured values of emission which are summed/integratedas a result of motion of the particle jet TX in relation to the locationand time, by means of which values it is also possible to calculate atwo-color pyrometric temperature and local distribution of the sametransversely with respect to the particle jet. By using a long exposuretime it is not, of course, possible to determine the temperatures ofindividual coating particles.

According to the principles shown in FIG. 7, a long exposure time inrelation to the velocity of the target must be used in signal-restrictedsituations, for example when the used spectroscopic method or theradiation properties of the target make it necessary to select thespectral bands corresponding to the filter areas so that they arespectrally very narrow, i.e. that they permeate a small amount ofradiation. The situation is of this kind when the aim is to measure onlythe radiation of fixed narrow spectral lines, or when the aim is toprevent certain spectral lines that are close to the measuringwavelengths and possibly interfere with the measurement from ending upin the same measuring result. In the aforementioned situation, when ashort exposure time is used and the aim is to distinguish e.g.individual particles, the signal integrated to the corresponding pixelsdoes not exceed the detection limit at all or its signal/noise ratioremains too low. If the method is based on the utilization ofspontaneous emission of the target itself, it is not, for example,possible to detect targets with too low a temperature by means of shortexposure times.

It is a considerable advantage of the present invention that insignal-restricted situations of the above kind for example pyrometrictwo-color temperature measurement can be conducted in an integratedmanner and using average values by utilizing long exposure time andspectral bands/filter areas selected optimally for said pyrometricmeasurement. With the same device it is now possible to conduct othermeasurements or visualization by using a different exposure time and therest of the unfiltered imaging area of the detector when necessary,and/or other spectral bands/filter areas optimized especially for othermeasurements or visualization in question.

The possibility provided by the invention to use various differentmeasurements or visualization in an optimized manner is illustrated inthe following, using the thermal spray coating process as an example.

According to the facts presented above, in FIGS. 6 and 7 the propertiesof spectral bands/filter areas FR1 and FR2 are selected to be suitablefor two-color pyrometric temperature measurement, and the measurementcan be conducted either for individual coating particles (FIG. 6) or forthe particle jet (FIG. 7) in an integrated manner by means of averagevalues, depending on the properties (e.g. temperature and/or particledensity) of the target. The essential fact is that from the situationaccording to FIG. 6 it is possible to easily and rapidly move to asituation according to FIG. 7 by changing the exposure time of thematrix detector.

In the situation of FIG. 6 it is possible to determine the velocity ofindividual particles by means of a so-called time-of-flight principleknown as such, when the exposure time used in the imaging and themagnification of the imaging optics are known. The measurement of thevelocity of particles can, in principle, be implemented at any point ofthe imaging area, because the measurement of velocity is not dependenton the brightness of images produced by individual particles, but onlyon the length of streaks drawn by the said particles in the image. Themeasurement of the velocity of particles can also be implemented byusing double or multi-exposure and by identifying the locations of theimages corresponding to each individual particle, and the distancesbetween said images which now correspond to the different exposures. Ifthe images/streaks of individual particles are signal-restricted at theexposure time used in the measurement of velocity, it is in a mannercharacteristic to the invention advantageous to conduct theidentification of the aforementioned images/streaks in the spectrallyunfiltered imaging area of the detector, which thus has the maximumsensitivity as a result of its spectral band which is as wide aspossible, i.e. unrestricted by filters.

In a manner corresponding to the above measurement of the particlevelocity and in a manner known as such it is, of course, in thesituation of FIG. 6, possible to determine the number of particlesdetected in the image in images taken successively, as well as indifferent parts of the imaging area. If the detection of particles issignal-restricted, it can also be advantageously conducted in thespectrally unfiltered imaging area of the matrix detector in a mannercharacteristic to the invention, or alternatively by using a longexposure time according to FIG. 7, wherein the number of particles indifferent parts of the imaging field, and especially the distributiontransverse to the direction of motion can be detected relatively on thebasis of the local brightness of the image, and by taking into accountthe temperature distribution transverse to the direction of motion (FIG.7), which is measured two-color pyrometrically at an earlier stage.

When the two-color pyrometric temperature of the coating particles isknown, which temperature can be determined according to the knownprinciples of pyrometry without the information on the size of theparticle, it is, according to prior art known as such, possible toobtain further information on the size of the particle by utilizing theintensity of radiance emitted by said particle on a known wavelengthband suitable for the purpose. In other words, the radiation emitted bya particle in a fixed temperature depends on the size of the particle,and if the temperature is known on the basis of the two-color pyrometricmeasurement, it is possible to calculate the size on the basis of theintensity of radiance of the particle. According to the invention, thismeasurement can be easily conducted by supplementing the system in thesituation according to FIG. 6, if necessary, with a third filter areaoptimized especially for this purpose.

When the thermal spray coating process according to FIG. 5 is imaged,one significant practical problem is caused by the large variations inbrightness occurring inside the imaging area, which set high demands forthe dynamical range of the matrix detector in use, in other words forits capability to measure/detect emission of different scales ofmagnitude. If the left edge of the imaging region ROI shown in FIG. 5 isplaced too close to the spraying device G, the brightness of the flame Pmay interfere with the actual detection of the coating particles bycausing overexposure of pixels corresponding to the left edge of theimaging region ROI on the screen of the matrix detector. According tothe invention this can be avoided by adding a separate filter area insaid point in the imaging area, which filter area attenuates theradiation coming from the target to said imaging area in a suitablemanner, thus reducing the requirements set for the dynamical range ofthe detector. When a process of another kind, for example a reactiveflow is imaged, the need for attenuation of radiation may also occur inthe direction of motion of the target in a different point in theimaging area than above, when the temperature of the target, theconcentration under examination, or other corresponding factor isincreased or changed in another manner as a result of the reactionsoccurring in the process.

As was already mentioned above, in thermal spray coating processes thelocal distribution of the parameters of the coating particles in theflame is also important in view of controlling and adjusting theprocess. For example in the situation shown in FIG. 5, when coatingparticles are fed in the form of powder along with so-called carrier gasfrom port I, if the flow rate of said carrier gas is adjusted too lowthe coating particles do not penetrate the hot inner parts of the flameP in the intended manner. In a corresponding manner when a high flowrate of the carrier gas is used, the coating particles penetratedirectly through the flame. In both cases the parameters of the coatingparticles hitting the target S, such as the temperature and velocitydeviate from the optimal values.

FIGS. 8 to 10 illustrate by means of examples ways of determining thelocal distributions of some parameters of coating particles in a thermalspray coating process that are made possible by the imaging methodaccording to the invention. It is, of course, obvious that the localdistributions of parameters measured at a given time within the scope ofthe inventive features presented in the claims can be determined in acorresponding manner in other kinds of processes.

FIG. 8 shows in principle the act of determining the local distributionDT of the two-color temperature of coating particles, transverse withrespect to the movement of the particles. The two filter areas markedwith a hatching in FIG. 8 and used in the process of determining thetemperature of the particles are further divided into smallerobservation areas R1 to RN, and the temperatures of individual particlesdetermined inside each observation area R1 to RN are calculated insidethe same either as instantaneous average values or average valuescumulative with respect to time, and said average values are utilized toform the distribution DT. Thus, it is possible to form an instantaneoustemporary distribution on the basis of one image taken by means of themeasuring device, or a cumulative distribution on the basis of severalsuccessive images.

FIG. 9 shows in principle the use of the entire imaging area of thematrix detector with respect to the movement of particles in defining adistribution DV transverse to the movement of particles, for example indefining the number distribution or velocity distribution of particles.Furthermore, FIG. 10 shows in a corresponding manner in principle theact of defining the distribution of the particles in the direction ofmovement, for example the number distribution or velocity distribution.

In FIGS. 8 to 10 the size of the observation areas R1 to RN used informing the distributions can vary according to the need, and they mayonly contain filter areas formed in the detector, or imaging arealocated outside the filter areas, depending on the parameter inquestion. In addition to the aforementioned distributions, it is, ofcourse, also possible to determine other statistics from theparameter/parameters defined from the target/targets by means ofimaging, if necessary.

The state of the thermal spray coating process and the function of thespraying apparatus can be controlled by monitoring the localdistributions of the essential measuring parameters that are formed inthe above-described ways and illustrate the state of the coatingparticles and thus the state of the process, and/or other statistics aswell as changes occurring in these distributions or statistics. Thecoating process can be adjusted further, if necessary, either manuallyor automatically by using said measurement results in such a manner thatoptimal operating conditions are attained. The visualization of thetarget that becomes possible by means of the invention, i.e. thereal-time image transmitted from the target to the operator alsofacilitates the control and adjustment of the process as such. Thevisualization facilitates and accelerates especially for example thepreliminary inspections and adjustments required in the process inconnection with the change of the wearing parts of the spraying device G(nozzles, etc) and/or coating material and/or coating material batch. Bymeans of visualization the imaging measuring device can also be directedaccurately to the desired location.

It is, of course obvious that the use of the invention is not restrictedsolely to the research, monitoring and adjustment of the thermal spraycoating process described above as an example, but within the scope ofthe inventive features presented in the claims it can also be applied inother processes that contain a moving or flowing target/moving orflowing targets.

Furthermore, within the field of spectroscopic methods, the use of theinvention is not restricted to the mere use of pyrometry, but otherimaging measurement methods can be advantageously implemented by meansof the invention. In addition to spectral definition, the differentfilter areas formed on the imaging area of the detector may also containproperties which are mutually dependent on the polarization of theradiation to be measured in different ways. The method for illuminatingthe target under examination is not significant in view of theinvention, but the target/targets to be examined can emit radiationthemselves and/or scatter radiation obtained from other sources.

It is, of course, obvious that in such situations in which thetarget/targets are detected on the basis of the radiation scattered bythe same, the movement of the target/targets in the image can be stoppedby using either a substantially continuously operating light source aswell as a sufficiently short shutter time in the detector at the sametime. Alternatively, by using a short light impulse/impulses, in otherwords stroboscopic illumination, it is possible to use a shutter timelong as such with respect to the velocity of the target/targets. In boththese ways it is possible to attain the same effective exposure timewith respect to the detection of the target, which fact is also statedin the claim by using the term effective exposure time instead of theterm exposure time.

When such a target is imaged which contains smaller targets that can bedistinguished separately on the imaging area DA, it is also possible touse two or more successive exposures instead of a single exposure in thedetection of said targets by means of the radiation emittedspontaneously by the same. For example in the situation of FIG. 6, thetargets depicted in streak-like form (e.g. T1 in FIG. 6) on the imagingarea DA of the detector would then be depicted as two or severalsuccessive dots each. The dots which are produced by one such target andwhich occur in the different filter areas can be used according to theinvention instead of the aforementioned streak to implementspectroscopic measurements.

When exposure sequences composed of three or more single (short)successive effective exposures (determined by the light impulse and/orthe shutter time of the detector) are used and one or more intervalsbetween the sequences are adjusted between said sequence so that theybecome different in size when compared to the other intervals, it ispossible to determine the direction of motion/flow of thetarget/targets. By using exposure sequences formed of four or severalsingle successive effective exposures, it is also possible to determinethe speed of change in other words acceleration or deceleration, in thevelocity of motion/flow of the target/targets.

The imaging measurements of the different parameters of the process canbe implemented substantially in real time by utilizing matrixdetector/camera apparatuses and computer apparatuses which are alreadycommercially available at present. For example by processing imagestaken at the rate of 25 images per second as a continuous process bymeans of an effective computer and image processing algorithms, it ispossible to use the parameters defined in this manner in the real-timemonitoring and control of the process under examination. In processessuch as thermal spray coating of certain targets inside a structure, themeasurement of which during the actual operation of the process isdifficult or impossible, the operation of the process device, forexample the operation of the spray coating device in particular, can berapidly ensured by means of imaging measurement immediately before andafter the actual process operation. If it is thus detected by means themeasured parameters that a change has occurred in the function of thespraying device, it is possible to interrupt the actual function of theprocess, if necessary, for adjustments and/or repairs of the sprayingdevice.

It is, of course, obvious that by producing a motion between the targetto be measured and the measuring device according to the invention bymeans of a suitable external method, it is also possible to conductmeasurements according to the invention for such targets which do notnaturally contain a moving or flowing target. Such methods can be forexample the act of moving or rotating the imaging measuring deviceitself, or correspondingly, the act of transmitting an image of thetarget via rotating or vibrating reflective optics.

In certain situations it is also possible that the use of only a singlefilter area added to the imaging area of the detector is sufficient forconducting a certain spectroscopic measurement. Thus, the so-calledunfiltered imaging area of the detector and the spectral response of thesame is used as one wide measurement wavelength band and within saidadded filter area there is another narrower measurement wavelength bandavailable, which is more precisely restricted but remains spectrallyinside the preceding one. This solution is, however, less advantageousin view of the solution according to the invention as a result of theobvious and restricted possibilities in the selection of said spectralbands.

1. A method for conducting an imaging, spectrally resolvingspectroscopic measurement of a moving or flowing target, in which methodthe electromagnetic radiation obtained from said target is focused bymeans of imaging optics to produce an image on the screen of atwo-dimensional matrix detector at least via a first and a second filterwhich transmit electromagnetic radiation in manners differing from eachother, wherein said at least first and second filter form on the screenof the detector at least a first and a second filter area that togetherpartly and only partly cover the light-sensitive area of the detector,and wherein the properties of at least one fixed part of the target aredetermined spectroscopically by comparing and/or combining spectrallyresolved information corresponding to said fixed part of the target andsaid information is recorded sequentially in time when an image pointwhich corresponds to said fixed part of the target and is focused on thescreen of the detector without beamsplitting travels as a result of themovement of the target substantially via said at least first and secondfilter area, and wherein the area of the screen of the detectorremaining outside said at least first and second filter area is used forat least one other imaging non-spectroscopic measurement and/orvisualization of the target.
 2. The method according to claim 1, whereinsaid at least first and second filter are located close to the screen ofthe detector, in front of the screen in the direction of incidence ofelectromagnetic radiation attained from the target, next to each othersubstantially on the same plane and substantially parallel to thescreen.
 3. The method according to claim 1, wherein said at least firstand second filter are located next to each other substantially on thesame plane with each other, and in the intermediate focus of the imagingoptics used in focusing electromagnetic radiation attained from thetarget.
 4. The method according to claim 1, wherein said at least firstand second filter area are located next to each other on the screen ofthe detector, not on top of each other but contacting each otherlaterally, or adjacently not on top of each other but apart from eachother.
 5. The method according to claim 1, wherein said at least firstand second filter area each cover an area which is macroscopic withrespect to single pixels of the detector.
 6. The method according toclaim 1, wherein said at least first and second filter area are alsoused for said imaging non-spectroscopic measurement and/or visualizationof the target.
 7. The method according to claim 1, wherein the effectiveexposure time of the detector used for detecting the target to be imagedis short in relation to the velocity of said target, and therefore,measured values describing the local and instantaneous state of saidtarget are obtained as a measurement result.
 8. The method according toclaim 1, wherein the effective exposure time of the detector used fordetecting the target to be imaged is long in relation to the velocity ofsaid target, and therefore, measured values summed/integrated inrelation to the location of said target and time are obtained as ameasurement result.
 9. The method according to claim 7, wherein saideffective exposure time is adjusted in such a manner that when thetarget is composed of individual targets which are distinguishableagainst their background and emit and/or scatter radiation, theimages/image streaks produced by said individual targets on the screenof the detector are substantially distinguishable from each other onsaid screen.
 10. The method according to claim 9, wherein thespectroscopic and/or non-spectroscopic method used in the measurement isapplied separately for each individual target distinguished separately.11. The method according to claim 1, wherein the parameter to bedetermined spectroscopically from the target that is imaged is thepyrometric temperature of said target or of smaller targets individuallydistinguishable inside said target.
 12. The method according to claim 1,wherein instantaneous or cumulative local distributions and/orstatistics of parameter/parameters defined from the target by means ofimaging are also determined.
 13. An imaging measuring device forspectrally resolving spectroscopic measurement of a moving or flowingtarget, which measuring device comprises at least an imagingtwo-dimensional matrix detector, at least a first and a second filter,and imaging optics for focusing electromagnetic radiation obtained fromthe target to be imaged on the screen of said detector via said at leastfirst and second filter which transmit electromagnetic radiation inmanners differing from each other, wherein said at least first andsecond filter are arranged to form on the screen of the detector atleast a first and a second filter area that together partly and onlypartly cover the light-sensitive area of the detector, and wherein thedevice further comprises means for determining the properties of atleast one fixed part of the target spectroscopically by comparing and/orcombining spectrally resolved information corresponding to said fixedpart of the target and recorded sequentially in time when an image pointwhich corresponds to said fixed part of the target and is focused on thescreen of the detector without beamsplitting is arranged to travel as aresult of the movement of the target substantially via said at leastfirst and second filter area, and wherein the device further comprisesmeans for using the area of the screen of the detector remaining outsidesaid at least first and second filter area for at least one otherimaging non-spectroscopic measurement and/or visualization of thetarget.
 14. The imaging measuring device according to claim 13, whereinsaid at least first and second filter are located close to the screen ofthe detector, in front of the screen in the direction of incidence ofelectromagnetic radiation attained from the target, next to each othersubstantially on the same plane and substantially parallel to thescreen.
 15. The imaging measuring device according to claim 13, whereinsaid at least first and second filter are located next to each othersubstantially on the same plane with each other, and in the intermediatefocus of the imaging optics used in focusing electromagnetic radiationattained from the target.
 16. The imaging measuring device according toclaim 13, wherein said at least first and second filter area are locatednext to each other on the screen of the detector, not overlapping butcontacting each other laterally, or adjacently not overlapping but beingapart from each other.
 17. The imaging measuring device according toclaim 13, wherein said at least first and second filter area each coveran area macroscopic with respect to the single pixels of the detector.18. The imaging measuring device according to claim 13, wherein said atleast first and second filter are manufactured on the front and/or rearsurfaces of a substantially transparent planar substrate material byapplying in the operating wavelength area of the detector one-layer ormultilayer coating/coatings that reflect and/or absorb/attenuateradiation.
 19. The imaging measuring device according to claim 13,wherein said at least first and second filter are made of colored glass.20. The imaging measuring device according to claim 13, wherein thematrix detector is a CCD matrix camera, a GaAs matrix camera or a CMOScamera.
 21. The use of information in monitoring or controlling aprocess, which information is measured by spectrally resolved imagingfrom a moving or flowing target to a two-dimensional matrix detector viaimaging optics and at least a first and a second filter transmittingelectromagnetic radiation in manners differing from each other, whereinthe properties of at least one fixed part of the target or smallertarget/targets which can be distinguished individually inside saidtarget are determined by means of imaging and spectroscopically bycomparing and/or combining signals, which are recorded sequentially intime when an image point which corresponds to said fixed part of thetarget/targets and is focused on the screen of the detector withoutbeamsplitting travels as a result of the movement of the target/targetssubstantially via at least a first and a second filter area which areformed on the screen of the detector by means of filters and whichpartly and only partly cover the light-sensitive area of said screen thearea of the screen of the detector remaining outside said at least firstand second filter area is used for at least one other imagingnon-spectroscopic measurement and/or visualization of the target. 22.The use according to claim 21, wherein said at least first and secondfilter area are also used for said imaging non-spectroscopic measurementand/or visualization of the target.
 23. The use according to claim 21,wherein the effective exposure time used in the imaging is adjusted tobe short in relation to the velocity of the target, so thatinstantaneous or local measured values of said target are recorded inthe measurement and/or smaller targets located individually in thetarget inside the imaging area are distinguished as being separate fromeach other.
 24. The use according to claim 21, wherein the effectiveexposure time used in the imaging is adjusted to be long in relation tothe velocity of the target, so that measured values summed/integrated inrelation to the location of said target are recorded.
 25. The useaccording to claim 21, wherein the pyrometric temperature of thetarget/targets is defined spectroscopically by means of spectrallyresolved imaging information.
 26. The use according to claim 21, whereinthe velocity of the target/targets is defined by means of imagingaccording to the time-of-flight principle by using either a single shorteffective exposure time or several successive short effective exposuretimes.
 27. The use according to claim 21, wherein the number ofindividual targets detected in the image by means of imaging isdetermined by utilizing the short effective exposure time.
 28. The useaccording to claim 21, wherein instantaneous or cumulative localdistributions and/or statistics of the parameter/parameters determinedfrom the target/targets by means of imaging are also defined.
 29. Theuse according to claim 21, wherein the process is a thermal spraycoating process.